redcloth (MissingSourceFile) - new problem after Heroku changed to bundler 1.0.7

Our app had been working. Now I just pushed some new code into staging on Heroku for the 1st time aft开发者_开发问答er they moved to bundler 1.0.7. Now our app crashes and I got this error message -

/usr/ruby1.9.1/lib/ruby/gems/1.9.1/gems/bundler-1.0.7/lib/bundler/runtime.rb:64:in `require': no such file to load -- redcloth (MissingSourceFile)

We're on Rails 2.3.8.

Here is part of the Gemfile -

gem 'rails',   '2.3.8', :require => nil
gem 'RedCloth',                   :require => 'redcloth'

Any ideas on how to fix this problem? Thanks.

I'm on Heroku and this is what I have :

gem 'RedCloth', '4.2.3'